This invention relates to a positive electrode of a lead acid battery, especially of a valve regulated type lead acid battery.
Conventionally, an electrode for lead acid battery has so far been classified roughly into two types: a tubular (clad) type and a paste type. The tubular type electrode has a structure composed of a core metal made of lead alloy, a cylindrical tube made by weaving a corrosion resistant glass fiber, and an active material retained by the tube, and has been used mainly for a positive electrode of a long-life battery. The paste type electrode has a sheet-shaped structure in which an active material is retained in a grid made of lead alloy, and has been used mainly for a negative electrode and a positive electrode for a battery excellent in high-rate characteristic and of low price.
In recent years, demands for a high energy density and a long service life have been increasing remarkably in a valve regulated type lead acid battery. However, since there has been a limitation for the high energy density to be in compatible with the long service life in the electrode of the above-mentioned type, the demands have not fully been satisfied. Namely, in the tubular type electrode, the active material is prevented from falling down even when the core metal is corroded because the active material is retained by the cylindrical tube made by weaving the glass fiber. Therefore, the service life is prolonged but the high-rate discharge characteristic is low because a reaction surface area of the electrode is not large, so that a high energy density can not be obtained. While, in the paste type electrode, the high-rate discharge characteristic is high because a reaction surface area becomes large owing to the sheet-shaped form so that a high energy density can be obtained. However, when the grid is corroded to change its shape, a contact of the grid with the active material can not be maintained and falling-off of the active material takes place, so that the long service life can not be accomplished.